The present invention relates generally to interface devices between humans and computers, and more particularly to computer interface devices that provide force feedback to the user.
Interface devices are used extensively with computer systems in the implementation of computer-controlled games, simulations, and other applications very popular with the mass market of home consumers. In a typical implementation, a computer system displays a visual environment to a user on a display device. Users can interact with the displayed environment by inputting commands or data from the interface device. Popular interface devices include joysticks, xe2x80x9cjoypadxe2x80x9d button controllers, mice, trackballs, styluses, tablets, pressure spheres, foot or hand pedals, or the like, that are connected to the computer system controlling the displayed environment. The computer updates the environment in response to the user""s manipulation of a moved manipulandum such as a joystick handle or mouse, and provides visual feedback to the user using the display screen.
In some interface devices, haptic (e.g., tactile) feedback is also provided to the user, more generally known as xe2x80x9cforce feedback.xe2x80x9d These types of interface devices can provide physical sensations to the user manipulating the physical object of the interface device. Typically, motors or other actuators of the interface device are coupled to the manipulandum and are connected to the controlling computer system. The computer system receives sensor signals from the interface device and sends appropriate force feedback control signals to the actuators in conjunction with host events. The actuators then provide forces on the manipulandum. A local microprocessor can be used to offload some computational burden on the host. The computer system can thus convey physical sensations to the user in conjunction with other visual and auditory feedback as the user is contacting the manipulandum. Commercially available force feedback devices include the ForceFX joystick from CH Products, Inc. and Immersion Corporation, and the Sidewinder Force Feedback Pro from Microsoft Corporation.
One problem occurring in the commercially available force feedback devices is that the motion transmission mechanisms in these devices are typically not ideal for transmitting forces. Well known motion transmission mechanisms such as a slotted bail tend to induce more friction and backlash than is desirable for conveying realistic and subtle force sensations. This limits the degree of sensitivity conveyed to the user through the actuators of the device, and as a result the user feels force sensations on such devices as less precise, immersive, and meaningful.
A different problem occurring in providing commercially available force feedback devices with realistic forces is providing a low cost device. Force feedback components, such as the transmission, tend to incur a large portion of the cost of manufacturing the device. For example, cable drives or capstan drives can offer high-bandwidth, amplified forces but are typically difficult to assemble, thus causing higher expense. Belt drives, in contrast, are typically easier to assemble and thus can provide amplified forces at a lower cost of production. However, belt drives that use tension or preload in the belt to transmit forces typically introduce a significant amount of friction and thus can be unsuitable for use in a force feedback device.
Non-tensioned belt drives do not use tension but instead engage the belt with pulleys using teeth or other positive grip elements, and thus have much less friction and are much more suitable for use in a force feedback device than tensioned belt drives. However, one problem occurring with the non-tensioned type of belt drives is that an amount of compliance is typically inherent in the system caused by slack in the belts. This slack can sometimes cause the belts to slip off or jump radially away from the drive pulleys or other pulleys in the drive system, causing loss of positive engagement and a concomitant loss in quality of force sensations. It can be a problem to prevent this movement and slippage without increasing the friction in the system.
The present invention provides a force feedback interface device which includes several improvements to the mechanical and force transmission system. One feature is the linkage mechanism disclosed herein that provides minimal backlash, friction, and compliance and allows the actuators of the system to be grounded. Other features include a belt drive mechanism including features to reduce the probability of the belt jumping off the drive mechanism.
More particularly, in one embodiment, a force feedback device of the present invention is coupled to a host computer and includes a user manipulatable object graspable by a user, two actuators operative to output a force in provided degrees of freedom, and at least one sensor operative to sense motion of the user manipulatable object in the degrees of freedom and which can be coupled to the actuators. A linkage mechanism is coupled between the actuators and the user object and provides the user object with first and second rotary degrees of freedom. The linkage mechanism includes a grounded member, a first extension member and a second extension member rotatably coupled to the grounded member, and a first central member rotatably coupled to the first extension member and a second central member rotatably coupled to the second extension member. The first and second central members are rotatably coupled to each other, and the first extension member and first central member are substantially identical to and positioned symmetrically to the second extension member and second central member.
The first and second extension members each preferably include two protrusions, where each of the protrusions is rotatably coupled to the first and second central members, respectively. Portions of the first and second extension members extend out of a plane formed by axes of rotation for the first and second degrees of freedom, where the portions that extend out of the plane are preferably a middle portion of at least one of the protrusions. At least one protrusion of the first extension member extends out of the plane on a first side of the plane, and at least one protrusion of the second extension member extends out of the plane on a second side of the plane opposite to the first side. The protrusions of the first extension member are rotatably coupled to the first central member such that the first central member is positioned between the protrusions, and a similar arrangement is provided for the second extension and central members. Some or all portions of the linkage mechanism and the drive mechanism, such as a belt drive, are preferably symmetrical and thus allows low cost manufacture of the device.
In a different aspect of the present invention, a force feedback device is coupled to a host computer and includes a user manipulatable object graspable by a user and moveable in at least one degree of freedom, at least one sensor operative to sense motion of the user object, and an actuator for outputting a force on the user object. A belt drive transmission is coupled between the actuator and the user object, and the belt drive transmission includes a drive pulley coupled to the actuator, an amplification pulley coupled to the drive pulley by a preferably synchronous belt, and an idler positioned adjacent to the drive pulley. The idler impedes radial displacement of the belt away from the drive pulley during normal operation without preloading the belt. The idler preferably is provided as two different types, a passive idler and an active idler. The passive idler does not contact the belt during operation, thus providing no friction, and prevents the belt from moving a significant amount radially off the drive pulley and losing engagement when the belt is so influenced due to slack or compliance in the belt. The active idler continually contacts the belt during normal operation and increases the wrap angle of the belt on the drive pulley to prevent the jumping of the belt as well as slippage. In a two-stage embodiment, one or more passive idlers can be included in the first stage of the belt drive transmission, and one or more active idlers can be included in the second stage. Both stages can include amplification pulleys to amplify the forces output by the actuator, where the first stage is provided between the actuator and the second stage.
The improvements of the present invention provide a more precise and quality force feedback device, yet also allow the device to be manufactured at a significantly lower cost for competitive consumer markets. Both the linkage mechanism and belt drive transmission provide high bandwidth, low friction, and low compliance and permit force sensations to be transmitted with high fidelity from grounded actuators. The linkage mechanism provides enhanced support of couplings moved during use of the device. The belt drive improvements also allow for a belt drive transmission that is more easily manufactured without introducing problems occurring with the belt drive due to slack in the belt. Furthermore, the device has many symmetrical components that can be duplicated and reused to create a functional device at a much lower cost.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing.